Immunoregulation in filariasis will be studied in inbred jirds, Meriones unguiculatus, infected with Brugia pahangi. Evaluation of immunologic reactivity will be achieved by both in vitro and in vivo analysis and manipulation of the immune system of infected animals. The specific aims will be initially to analyze the development of immunoregulatory activity to specific antigens of B. pahangi over the course of infection of jirds with filariae. Subsequently, characterization of the cell(s) responsible for mechanisms of immunoregulation, the factors of host and/or parasite origin which stimulate the immunoregulatory activity and the immune capabilities of the host which may be altered will be attempted. In addition, the effect of modifying immunoregulatory activity by use of drugs or immunologic factors or cells on the immunological and parasitological status of the host will be analyzed. Evaluation of immunologic reactivity will rely primarily upon analysis of in vitro lymphocyte blastogenesis. Alterations in immunologic reactivity have been suggested to contribute to host susceptibility to filariasis and subsequent expression of disease. Consequently, gaining an understanding of immunoregulation in filariasis will help delineate methods by which the infection and disease may or may not be controlled or eradicated.